Tracking antenna system

ABSTRACT

A tracking antenna system utilizing a sum and a difference signal of radio wave signals received by a pair of antennas. A control unit controls signals based upon the sum and difference signals to always bring them into in-phase relationship and adds the signals thus controlled, whereby a radio wave from a source is received always at its maximum sensitivity.

United States Patent Takao et a].

TRACKING ANTENNA SYSTEM Inventors: Kazuakl Takao, Kyoto; Masakazu Takeuchi, Amagasaki, both of Japan Assignee: Mitsubishi Denki Kabushiki Kaisha,

Tokyo, Japan Filed: Sept. 15, 1970 Appl. No.: 72,339

Foreign Application Priority Data [56] References Cited UNITED STATES PATENTS 2,955,199 10/1960 Mindes ..343/1 17 A 7/1959 Melton ..343/100 CL Primary Examiner-Malcolm F. Hubler AttorneyRobert E. Burns and Emmanuel J. Lobato Sept. 22, 1969 Japan ..44/75435 [57] ABSTRACT U s C| 343/117 A 343/7 A 343/16 M, A tracking antenna system utilizing a sum and a dif- 343/113 R ference signal of radio wave signals received by a pair Int. Cl ..G01s 3/42 of antennas- A Control unit Controls Signals based Field of Search ..343/113 R, 117 A, upon the Sum and difference Signals to always bring 343 7 A, 1 M them into in-phase relationship and adds the signals thus controlled, whereby a radio wave from a source is received always at its maximum sensitivity.

4 Claims, 7 Drawing Figures m fi v COMPAR 1 251 5,0 l LOOP P 1 FLT 4 DET 48 1 PH -4 DET 1 36A 4011 i POLAR- 1 sw I i 408! ADDER 90 POLAR- I TO RECEIVER UNIT PHASE ITY 8 SHIFTER sw 46 I 1 I 368 35 PH 42B DET Q i TRACKING ANTENNA SYSTEM BACKGROUND OF THE INVENTION l. Field of the Invention This inventin relates to tracking antenna systems capable of tracking a radio wave signal source such as a flying missile so as to receive the radio wave from the signal source at its maximum sensitivity.

2. Description of the Prior Art As a tracking system of this kind, the one whose antenna is mechanically rotated in accordance with the movement of the signal source has first come to the fore. The system utilizes a sum and difference signals of the radio wave signals received by a pair of antennas (one type of signal to each of the pair) to produce an analog signal having a polarity depending upon the phase relationship as well as the relationship in signal intensity between the sum and difference signals. Through the use of the analog signal thus produced, the antenna system is mechanically rotated to face the direction in which the sensitivity of the antenna is at its maximum with respect to the incoming radio wave. However, the system as above outlined has disadvantages that the mechanism for rotating the antenna is complicated and that an accurate and rapid tracking is difficult to be achieved.

In order to eliminate the above disadvantages of the rotating antenna type systems, there has also. been proposed an antenna system wherein one of the pair of antennas is equipped witha radio wave phase shifter or a microwave phase shifter. The radio wave phase shifter used in the system serves to phase shift the radio wave signal through the use of the analog signal as previously described so as to cause the sensitivity of the antenna with respectto the incoming radio wave to reach its maximum. According to the antenna system of this type, although the antenna is not required to be mechanically rotated, another problem arises in the associated phase shifter. More specifically, the phase shifter is so arranged that either one of the phase shifters exhibiting various amounts of phase shifts is selected, or, otherwise, a rotary type phase shifter (continuously variable phase shifter) is used, in order to change the amount of phase shift in accordance with the movement of the signal source. This arrangement, however, is also disadvantageous in that the system becomes complicated in structure and that the tracking speed is not so high as required. In addition, since the typical phase shifter of this type is made of ferrite, the phase shifter is apt to change in the amount of phase shift depending upon the change in ambient temperature, leading to a disadvantage that an accurate tracking operation is difficult to be achieved.

Accordingly, an object of the inventio is to provide a new and improved tracking antenna system with a simple construction which uses neither the mechanical rotation of the antenna nor the radio wave phase shifter capable of performing a rapid and accurate tracking of a signal source.

SUMMARY OF THE INVENTION According to the present invention there is provided a tracking antenna system comprising at least one antenna pair, a hybrid junction coupled to said antenna pair to produce a sum signal and a difference signal of radio wave signals received by each of antennas of said antenna pair, and control means for controlling a first signal based upon said sum signal and a second signal based upon said difference signal to always bring these two signals into in-phase relationship and for adding said first and second signals.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a block diagram showing the tracking antenna system constructed in accordance with the invention;

FIG. 2 is a graph showing the sum and difference signals supplied from the hybrid junction employed in the system shown in FIG. 1;

FIG. 3 is a block diagram showing another embodiment of the invention;

FIG. 4 is a graph showing the sum and difference signals supplied from the hybrid junctions employed in the system shown in FIG. 3;

FIG. 5 is a characteristic diagram for showing sensitivity pattern of the antenna system shown in FIG. 3',

FIG. 6 is a schematic diagram showing the disposition of antennas for use in still another embodiment of the invention;

FIG. 7 is a schematic diagram showing the antenna disposition for use in another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing for a more detailed understanding of the invention, and in particular, to FIG. 1, an antenna array generally designated by the reference numeral 10 comprises a pair of antennas l2 and 14 spaced a distance d apart from each other. The antennas l2 and 14 are coupled to each other at the lower portion of the antenna array 10 by a hybrid junction 16 which may be a micro strip type coupler or the so-called magic T coupler. The hybrid junction 16 has first and second output terminals 18 and 20 respectively, the first output terminal 18 provides a sum signal V I of the radio wave signals each received by the respective antennas 12 and 14, and, on the other hand, the second output terminal 20 provides a difference signal V of the radio wave signals .each received by the respective antennas 12 and 14.

FIG. 2 shows amplitudes of and phase relationship between the sum and difference signals V; and V with respect to the incident angle 0 of the incoming radio wave. The incident angle .0 of the radio wave is measured from a geometric central axis 0--0 of the antenna array which is perpendicular to a line connecting the antennas l2 and 14 and on a plane including both the antennas l2 and 14.

The relationships between the sum and difference signals V and V A and the incident angle 6 are given by the following equations:

V; acos(/ 2) V asin(/ 2) where,

=kd sin 0 k=21r/ A wave length .of incoming radio wave, and d= distance between antennas.

In FIG. 2, there are shown four ranges of angles A A A and A each range corresponding to 90. More ---specifically, the ranges A, to A, range from -l80 to 90, 90 to from 0 to +90, and from +90 to" +1 80 respectively. It is also seen that the sum signal V; is of minus phase and the difference signal VA is of minus phase within the range A,. Within the range A,, the sum signal V 1 is of plus phase and the difference signal V is of minus phase; within the range A,, the sum signal V; is of plus phase and the difference signal V is of plus phase; and within the range A, the sum signal V; is of minus phase and the difference signal V is of plus phase. It is to be noted that the plus" and minus" denote that these signals are in the inverted phase relationship to each other.

FIG. 2 also shows that the amplitudes of the signals V and VA vary in accordance with the change of the incident angle 8 of the incoming radio wave. For example, when the incident angle 6 is 0 the amplitude of the signal V; is a, while that of the signal V is a,. in FIG. 2, the amplitudes a, and a, are shown as heights of the curves at the incident angle 6 The above description of the sum and differences signals V: and V has been made in terms of the changes in phase and in amplitude with respect to the incident angle 0 of the incoming radio wave, therefore, it is to be noted that plus and minus" in phase shown in FIG. 2 denote the phase relationship with respect to the incident angle 6. Considering the phase relationship with respect to the incident angle 0 between the sum and difference signals V); and V A together with the phase relationship with respect to time between the sum and difference signals V; and V both the sum and difference signals V; and V are of minus phase while the difference signal V is delayed by a phase angle of 90 with respect to the sum signal V; within the range A,. Similarly, the phase delay of 90 is always present in the differences signal V with respect to the sum signal V; also within the ranges A A and A i I Referring back to FIG. 1, there is illustrated a control unit generally designated by the reference numeral 30 is shown as encircled by a dotted line.- This control unit from the mixers 34A and B are equal in phase to' the sum and difference signals V; and V respectively. The intermediate frequency output are, in turn, am-

' plifiedby intermediate frequency amplifiers 36A and B. The output from the intermediate amplifier 36A will be called hereinafter a first signal V,.

The output from the intermediate frequency amplifier 36B is supplied to a 90 phase shifter 38 whose function is to compensate the time delay of 90, therefore, the 90 phase shifter 38 provides an output or a second signal V, which is compensated by a time delay of 90. It is to be recalled that the difference signal V is always delayed in time by an angle of 90 as compared with the sum signal V Thus the 90 phase shifter 38 brings the difference signal V into in-phase relationship in terms of time with the sum signal V; As a result, within the ranges A, and A the first and second signals V and V, are brought into in-phase relationship with each other, while within the ranges A and A, the first and second signals V, and V are brought into inversed-phase relationship with each other; i.e., they are out of phase by an angle of 180.

The control unit further comprises polarity switches 40A and B, phase detectors 42A and B, and a comparison signal generator 44. The polarity switches 40A and B have a function similar to 180 phase shifters. The first and second signals V, and V passing through the polarity switches 40A and B are phase-detected by the phase detectors 42A and B respectively through the'use of acompariso'n signal V which is supplied from the comparison signal generator 44. The comparison signal V is, for example, in in-phase relationship with the first signal V, which appears when the sum signal V; shown in FIG. 2 is of plus phase.

Therefore, when the sum signal V is of plus phase, the first signal V, passing through the first polarity switch 40A is borught into in-phase relationship with the comparison signal V and therefore the first phase detector 42A prevents the polarity switch 40A from being operated. As a result, in this case, the first signal V is passed through the polarity switch 40A without being phase shifted by it and is supplied to an adder 46 whose function willbe described in more detail later On the other hand, when the difference signal V is v of plus phase, the second signal V passing through the 12 and 14. The control unit 30 also comprises a socalled mixers 34A and B which convert the signal frequency to the intermediate frequency. The first mixer 34A receives at its input terminals the sum signal V from the first output terminal'l8 of the hybrid junction 16 and the reference signal V, supplied from' second polarity switch 40B isjn in-phase with the comparison signal V This is because the 90 phase shifter 38 has brought the second signal V passing through the polarity switch 408 into in-phase relationship with the first signal V, which appears when the sum signalV is of plus phase. Therefore, in this case, the second phase detector 428 prevents the polarity switch 408 from operating to deliver the second signal V through the polarity switch'40B without producing any shift in phase to the adder 46.

With the sum signal V;- which is of minus phase as in the case illustrated in'FlG. 2, the polarity switch 40A is brought into its operable state by the phase detector 42A to shift the first signal V, passing through the polarity switch 40A by an angle of or invert in phase. This results in the polarity switch 40A providing an output signal which is in in-phase relationship with the signal V, derived from the sumsignal V: of plus phase even when the sum signal V is of minus phase.

Similarly, with the difference signal V A of minus phase as in the case shown in FIG. 2, the polarity switch 408 is brought into its operable state by the phase detector 42B to shift the second signal V passing through the polarity switch 408 by an angle of 180 or invert in phase, thereby to provide an output signal which is in in-phase relationship with the signal V, based upon the difference signal VA of plus phase.

The signals V and V, passing through the polarity switches 40A and B and thus controlled in phase are supplied to the adder 46 of the conventional design.

The adder 46 adds the input signals V and V, to provide an output to a receiver unit (not illustrated) of the conventional design.

From the foregoing description, it is easily understood that the output from the adder 46 is always at its maximum in the direction of the incident angle 6 of the incoming radio wave. For example, in the case the incident angle 0 is of an angle 0, which is an angle within the range A the first signal V based upon the sum signal V 2 exhibiting an amplitude a as illustrated in FIG. 2, and the second signal V,, based upon after the first and second signals V and V have been added by the adder 46, they increase in intensity. Similarly, when the incident angle 0 of the incoming radio wave falls within any one of the ranges A A, or A the first and second signals V and V, based upon the sum and difference signals V 2 and V A respectively are added by the adder 46 after they have been brought into the in-phase relationship with each other, whereby the adder 46 always provides a high output to the receiver unit. Thus the tracking antenna system of the present inventioncan perform the tracking operation wherein the radio wave beamed from the moving signal source is always receivedat the maximum sen-- sitivity.

To transmit a radio wave through the use of the antenna system of the invention, the polarity switches 40A and B are operated in response to the ranges of angles in which the target to be aimed at exists. This enables the radio wave transmitted from the antenna array to always beam accurately at the target at its maximum intensity. I

The control unit further comprises a third phase detector 48 and a loop filter 50 which form a phase lock loop. The phase detector 48 phase detects the output from the adder 46 with respect to the comparison signal V When'the radio wave coming into the antenna array 10 varies in frequency, the phase relationship which has been extablished between the output from the adder 46 and the comparison signal V may become lost and result in the signals V and V, becoming out of phase with each other. To remove this inconvenience the phase detector 48 generates a dc. output having a polarity depending upon the direction of the phase shift and having a magnitude proportional to the amount of the phase shift as compared with the comparison signal V,. The dc. output from the phase detector 48 is supplied through the loop filter 50 to the reference signal generator 32 to change the oscillation frequency of the signal generator, thereby to maintain the output from the adder 46 in the in-phase relationship with the comparison signal V FIG. 3 shows another embodiment of the present invention capable of performing a tracking operation exhibiting a higher sensitivity. As seen from the FIGURE, the tracking antenna system comprises a plurality of antenna arrays 101, 102,... and 10N, each composed of a pair of'antennas 121 and 141, 122 and 142,..., and 12N and 14N respectively. Assuming that the distances between the respective antennas 121 and 141, 122 and 142,..., and 12N and 14N are d d d respectively, each of the antennas is disposed such that the relationship d d, d is held. The antenna array 101 is provided with a hybrid junction 161 having a first and second output terminals 181 and 201. Similarly, the antenna arrays 102 to 10N have hybrid junctions 162 to 16N respectively which also have respective first and second output terminals 182 and 202 and 18N and 20N. The hybrid junctions 161 to 16N are of the construction identical to the hybrid junction 16 which has been previously described in conjunction with FIG. 1. Therefore, the first output terminals 181, 182,...., 18N provide sum signals V 2 V 2 V 2 N of the incoming radio wave received by each of the antennas respectively, and the second output terminals 201, 202,-20N provide difference signals V A V A V A .of the incoming radio wave from the signal source respectively as in the case of the first embodiment previously described. The sum and difference signals V; and VA] supplied from the hybrid junction 161 through the first and second output terminals 181 and 201 respectively are provided to a control unit generally designated by the reference numeral 301. Similarly, the sum anddifference signals V 2 2 and V A and V 2 N and V A N provided from the respective hybrid junctions 162 and 16N are supplied through the output terminals 182 and 202, and 18N and 20N to control the units 302 and 30M respectively. The control units 301,

302, 30N are of the construction similar to those described in conjunction with FIG. 1 excepting that the reference signal generator 32, comprison signal generator 44, and third phase detector 48 and loop filter 50 incorporated in the control unit 301 are used in common with the other control units 302 to 30N inclusive. In order to obtain an output signal which is to be supplied to a receiver unit (not shown), all the output signals from the adders 46 each involved in the control unit 301, 302, 30N are added by an adder 600.

FIG. 4 shows the relationships between the sum signals V 2 V 2 V 2 N and the difference signals V A V A V A N respectively in amplitude and in phase with respect to the incident angle 6 of the incoming radio wave. As seen from the' FIGURE, the variation in the intensity of the signals V z and V 2 from the second antenna array 102 with respect to the incident angle 0 of the incoming radiowave is shorter in the cycle of variation as compared with the variationin the intensity of the signals V 2 1 and V A 2 derived from the first antenna array 101. It is also seen that the cycle of the variation of the signals V 2 N and V A N is shorter than those of the other signals. This will be easily understood by putting the relation of cl d d into the equations previously described. I

The control units 301, 302, 30N operate similarly to the control unit 30 previously described in conjunction with FIG. 1. More specifically, the control units 301, 302,-, 30N control the sum signals V 2 V 2 V 2 N and the difference signals V A V A V A N respectively to cause the respective sum and difference signals to be brought into the in-phase relationship as well as into the same polarity relationship independent of the variation in incident angle 6 of the incoming radio wave. Under the above control,,the control unit 301 provides an output signal which is an added signal of the signals based upon the sum and difference signals V 2 and V A and the control unit 302 provides an output signal which is an added signal of the signals based upon the sum and difference signals V and V and similarly, the control unit SUN provides an output signal which is an added signal of the signals based upon the sum and difference signals V N and V A As a result, each of the output from the control units 301, 302, 30N. is controlled to exhibit a common polarity and a common phase independent of the variation of the incident angle 0. These outputs from the control units 301, 302, 30N are added by the adder 600 to produce an output to be supplied to an unillustrated receiver unit.

FIG. 5 shows a sensitivity pattern of the antenna system shown in FIG. 3 under the condition of the incident angle .8 of the incoming radio wave being 6,. From the FIGURE, itis apparent that the sensitivity is at maximum at this incident angle 9 FIGS. 6 and 7 illustrate antenna arrays for use with another embodiment capable of performing a tracking operation in the three-dimensional space. It is seen in FIG. 6 that six antennas 121A, 122A, 123A, 141A, 142A and 143A are disposed on a first plane including a geometric central axis 00 and that the other six antennas 121B, 122B, 1238, 14113, 1428 and 1435 are disposed on a second plane including the geometric central axis 00 and perpendicular to the first plane. In FIG. 7, the antennas as shown in FIG. 6 are disposed on a circle. lnboth the antenna arrays shown in FIGS. 6 and 7, each of the antennas 1 21A and l4lA,'l22A and 142A, 123A and 143A, 1218 and 141B, 1228 and 1428, and 1233 and 1438 is coupled by-the hybrid junction identical to those previously described to form antenna pairs. It is to be understood that the antennas are disposed symmetrically with respect to the geometric central axis 00, while, in FIG. 6, the distances between the antennas are different from one another according to the respective antenna pairs. I

As similar to the antenna system shown in FIG. 3, the antenna arrays shown in FIGS. 6 and 7 are connected to the respective control units (not shown) identical to the previously described control units 301 to 30N inclusive through the hybrid junctions of the same construction as described in conjunction with FIG. 1. The control units are, in turn, connected to the adder as was the previous embodiment shown in FIG. 3. Therefore, similarly to the previous embodiments, the incoming radio wave from the signal source is controlled by the control unit for each of the antenna pairs to be brought into the in-phase relationship with each other and controlled to exhibit a common polarity independent of the variation of the incident angle 0 of the incoming radio wave. As a result, the control units provide output signals, each exhibiting a common phase and a common polarity to each other, which are-added by the adder.

It is easily understood from the disposition of the antenna arrays that the antenna systems shown in FIGS. 6 and 7 can perform the tracking in the three-dimensional space. Although the embodiments shown in FIGS. 6 and 7 have six antenna pairs, it is to be understood that the invention is also applicable to antenna systems having more or less than six antenna pairs.

What we claim is:

l. A tracking antenna system comprising at least one antenna pair, a hybridjunction coupled to said antenna pair to produce a sum signal and a difference signal of radio wave signals received by each of antennas of said antenna pair, control means for controlling a first signal based upon said sum signal and a second signal based upon said difierence signal to always bring the first and second signals into in-phase relationship and for adding them, said control means comprising a first detector for phase-detecting said first signal with a comparison signal, a second phase detector for phase-detectingsaid second signal with said comparison signal, a first polarity switch for phase-shifting said first signal by an angle of 180 in response to an output from said first phase detector, a second polarity switch for phase-shifting said second signal by an angle of 180 in response to an output from said second phase detector, and an adder for adding the outputs from said first and second polarity switches.

2. A tracking antenna system comprising at least one antenna pair, a hybrid junction coupled to said antenna pair to produce a sum signal and a difference signal of radio wavesignals received by each of the antennas of signal, a first polarity switch for phase-shifting said firstsignal by an angle of 180 in response to an output from said first phase detector, a second polarity switch for phase-shifting said second signal by an angle of 180 in response to an output from said second phase detector, :1 reference signal generator for providing a reference signal, a first mixer for providing said first signal in response to an intermediate frequency output produced based upon said sum signal and said reference signal, a second mixer for providing said second signal in response to an intermediate frequency output produced based upon said difference signal and said reference signal, and an adder for adding outputs from said first and second polarity switches.

3. A tracking antenna system comprising at least one antenna pair, a hybrid junction coupled to said antenna pair to produce a sum signal and a difference signal of radio wave signals received by each of antennas of said antenna pair, and control means for controlling a first signal based upon said sum signal and a second signal based upon said difference signal to always bring the first and second signals into in-phase relationship and for adding them, said control means comprising a first phase detector for phase-detecting said first signal with a comparison signal, a second phase detector for phasedetecting said second signal with said comparison signal, a first polarity switch for phase-shifting said first produced based upon said sum signal and said reference signal, a second mixer for providing said second signal in response toan intermediate frequency output produced based upon said difference signal and said reference signal, a phase shifter for phase shifting an output from said second mixer by an angle of 90 to produce said second signal, thereby to compensate a phase shift of 90 between said sum signal and said difference signal, and an adder for adding the outputs from said first and second polarity switches.

4. A tracking antenna system comprising at least one antenna pair, a hybrid junction coupled to said antenna pair to produce a sum signal and a difference signal of radio wave signals received by each of antennas of said antenna pair, and control means for controlling a first signal based upon said sum signal and a second signal based upon said difference signal to always bring the first and second signals into in-phase relationship and for adding them, said control means comprising a first phase detector for phase-detecting said first signal with a comparison signal, a second phase detector for phasedetecting said second signal with said comparison signal, a first polarity switchfor phase-shifting said first signal by an angle of in response to an output from said first phase detector, 21 second polarity switch for phase-shifting said second signal by an angle of 180 in response to an output from said second phase detector, a reference signal generator for providing a reference signal, a first mixer for providing said first signal in response to an intermediate frequency output produced based upon said sum signal and said reference signal, a second mixer for providing said second signal in response to an intermediate frequency output produced based upon said difference signal and said reference signal, an adder for adding the outputs from said first and second polarity switches, and a third phase detector for phase-detecting an output from said adder with said comparison signal, said third phase detector controlling the frequency of said reference signal thereby to lock the phases of said first and second signals. 

1. A tracking antenna system comprising at least one antenna pair, a hybrid junction coupled to said antenna pair to produce a sum signal and a difference signal of radio wave signals received by each of antennas of said antenna pair, control means for controlling a first signal based upon said sum signal and a second signal based upon said difference signal to always bring the first and second signals into in-phase relationship and for adding them, said control means comprising a first detector for phase-detecting said first signal with a comparison signal, a second phase detector for phase-detecting said second signal with said comparison signal, a first polarity switch for phaseshifting said first signal by an angle of 180* in response to an output from said first phase detector, a second polarity switch for phase-shifting said second signal by an angle of 180* in response to an output from said second phase detector, and an adder for adding the outputs from said first and second polarity switches.
 2. A tracking antenna system comprising at leasT one antenna pair, a hybrid junction coupled to said antenna pair to produce a sum signal and a difference signal of radio wave signals received by each of the antennas of said antenna pair, control means for controlling a first signal based upon said sum signal and a second signal based upon said difference signal to always bring the first and second signals into in-phase relationship and for adding them, said control means comprising a first phase detector for phase-detecting said first signal with a comparison signal, a second phase detector for phase-detecting said second signal with said comparison signal, a first polarity switch for phase-shifting said first signal by an angle of 180* in response to an output from said first phase detector, a second polarity switch for phase-shifting said second signal by an angle of 180* in response to an output from said second phase detector, a reference signal generator for providing a reference signal, a first mixer for providing said first signal in response to an intermediate frequency output produced based upon said sum signal and said reference signal, a second mixer for providing said second signal in response to an intermediate frequency output produced based upon said difference signal and said reference signal, and an adder for adding outputs from said first and second polarity switches.
 3. A tracking antenna system comprising at least one antenna pair, a hybrid junction coupled to said antenna pair to produce a sum signal and a difference signal of radio wave signals received by each of antennas of said antenna pair, and control means for controlling a first signal based upon said sum signal and a second signal based upon said difference signal to always bring the first and second signals into in-phase relationship and for adding them, said control means comprising a first phase detector for phase-detecting said first signal with a comparison signal, a second phase detector for phase-detecting said second signal with said comparison signal, a first polarity switch for phase-shifting said first signal by an angle of 180* in response to an output from said first phase detector, a second polarity switch for phase-shifting said second signal by an angle of 180* in response to an output from said second phase detector, a reference signal generator for providing a reference signal, a first mixer for providing said first signal in response to an intermediate frequency output produced based upon said sum signal and said reference signal, a second mixer for providing said second signal in response to an intermediate frequency output produced based upon said difference signal and said reference signal, a phase shifter for phase shifting an output from said second mixer by an angle of 90* to produce said second signal, thereby to compensate a phase shift of 90* between said sum signal and said difference signal, and an adder for adding the outputs from said first and second polarity switches.
 4. A tracking antenna system comprising at least one antenna pair, a hybrid junction coupled to said antenna pair to produce a sum signal and a difference signal of radio wave signals received by each of antennas of said antenna pair, and control means for controlling a first signal based upon said sum signal and a second signal based upon said difference signal to always bring the first and second signals into in-phase relationship and for adding them, said control means comprising a first phase detector for phase-detecting said first signal with a comparison signal, a second phase detector for phase-detecting said second signal with said comparison signal, a first polarity switch for phase-shifting said first signal by an angle of 180* in response to an output from said first phase detector, a second polarity switch for phase-shifting said second signal by an angle of 180* in response to an output from said second phase detector, a reference signal generatOr for providing a reference signal, a first mixer for providing said first signal in response to an intermediate frequency output produced based upon said sum signal and said reference signal, a second mixer for providing said second signal in response to an intermediate frequency output produced based upon said difference signal and said reference signal, an adder for adding the outputs from said first and second polarity switches, and a third phase detector for phase-detecting an output from said adder with said comparison signal, said third phase detector controlling the frequency of said reference signal thereby to lock the phases of said first and second signals. 